If the bacterial electron transport chain is located in the plasma membrane and the proton gradient is from outside the cell (high conc.) to inside (low conc.), then if bacteria are cultured in a medium slightly more acidic than normal, their rate of growth should increase. Am I right? Since, they'll make more ATP free of cost!

Also, bacteria are killed by gastric acidity. Does that have to do with protein denaturation owing to very low pH?